1. Field of the Invention
The present invention relates to a ceramic composite material with high heat-resistant property to be used in the application where high heat-resistant property is required, and in particular to a ceramic composite material with high heat-resistant property, which can be used at 1500.degree. C. or more and has high resistance to oxidation, high creep resistance and excellent high temperature strength under atmospheric conditions.
2. Description of Prior Art
In the past, ceramic materials such as SiC and Si.sub.3 N.sub.4 have been used for high temperature applications where metals cannot be used. However, these ceramic materials are usually produced by powder molding and sintering processes, and products are often subject to extensive shrinkage and deformation during manufacture. For this reason, further fabrication to finish the product shape is needed, and this leads to high manufacturing cost of the ceramic products.
In general, sintering of heat-resistant material is very difficult to perform, and auxiliary agents to assist sintering must be added to obtain dense products. It is known, however, that these auxiliary agents give adverse effect to mechanical property of the material at high temperature.
On the other hand, reaction sintering method or infiltration method are advantageous in that no shrinking or deformation occurs almost at all during fabrication and dense products can be obtained. For this reason, SiC-Si type materials are widely used in industrial application. These materials are easy to manufacture and have high resistance to oxidation and comparatively high strength. However, metallic Si having melting point of about 1400.degree. C. remains in the structure, and high temperature strength rapidly decreases at temperature of 1300.degree. C. or higher, and these materials cannot be used as structural material at higher temperature.
For this reason, a composite material has been developed by infiltrating MoSi.sub.2 having higher melting point and very high resistance to oxidation into SiC (Journal of Materials Science, Vol. 24, pp. 4144-4151; 1989). Because this composite material is manufactured by infiltration method, there is no need to use auxiliary agents, which impair high temperature property. Thus, this material has high resistance to oxidation at high temperature and excellent high temperature strength and can be produced by near-net shape fabrication. However, melting point of MoSi.sub.2 is 2000.degree. C. or higher, it is disadvantageous in that high manufacturing temperature is required.
To overcome this drawback, a method has been proposed. According to this method, Si-Mo melt is infiltrated into SiC preform, which contains carbon (Journal of the American Ceramic Society, Vol. 73, No. 5, pp. 1193-1200; 1990). By this method, exothermic reaction of silicon and carbon is utilized, and it is possible to manufacture SiC-MoSi.sub.2 type composite materials at relatively low temperature of about 1600.degree. C. In this case, however, composition of melt changes as reaction advances, and it is necessary to elaborately assess and control composition and size of the preform and composition of melt, and this is not suitable for industrial application.
In SiC-MoSi.sub.2 composite materials, surface is covered with silica glass film due to high temperature oxidation, and this leads to high resistance to oxidation. The glass film crystallizes over time, and glass film is cracked due to difference of thermal expansion coefficient during cycles of temperature increase and decrease. In some cases, film spalls off, and resistance to oxidation is reduced.